A block copolymer, according to the description of “Chemical Dictionary (popular edition) edited by Seiji Shida, published by Morikita Publishing Co., Ltd. in 1985,” is “a polymer that polymer segments having different chemical structures of two kinds or more in a molecule are mutually linked,” for example, a block copolymer containing a hard segment wherein a polymer chain is rigid and a soft segment wherein a polymer chain is flexible, has variously been developed as a block copolymer with strength and toughness. Regarding such block copolymer having polymer segments (hereinafter abbreviated as “segment”) with contradictory properties each other, physical properties of the block copolymer vary easily depending on the chain length of segment and repeating degree, thus an analysis technique effective for a quality control on its production is important to obtain a block copolymer with a stable quality.
As a method for producing the block copolymer, examples include a method that after obtaining polymers which can be segments of two kinds or more (segment precursor polymers) each by polymerization, these are linked; and a method that a segment precursor polymer having a reactive group at the terminal is produced beforehand, and a monomer inducing the other segment is sequentially polymerized with the precursor polymer. In these production methods, a technique that quality of segments constituting a block copolymer is controlled by conducting a polymer analysis at a stage of a segment precursor polymer which a production intermediate to produce a block copolymer of a final product stably, is ordinarily used. However, a practical method for analyzing and evaluating segments constituting the copolymer after obtaining a block copolymer is hardly developed.
As a typical example of analysis techniques on each segment constituting a block copolymer, for a styrene-butadiene copolymer, a method for analyzing a polystyrene segment by ozone decomposition of a polybutadiene segment, is proposed (for example, see “Y. Tanaka, et. al.: Rubber Chem. Yechnol., 59, 16 (1986)”). However, since ozone is highly reactive, unless the conditions are strictly controlled, ozone decomposition itself is poorly reproducible, so it is not sufficient for an analysis method aiming at quality control. Application of ozone decomposition is limited to a polymer derived from diene and a polymer having a polyalkylene oxide chain (for example, see “new edition, Polymer Analysis Handbook, published by Kinokuniya Company Ltd. in 1994”), and there is almost no example of the application to other polymers at present.
By the way, an attention is drawn to an aromatic block copolymer in applications such as ion-conducting membrane, oxygen-permeating membrane and ion-exchange membrane, being suitable in terms of mechanical strength and heat resistance, and exhibiting functionalities on phase separation when formed in a film shape. In the developments of aromatic block copolymers with higher performance, in particular, a technique for a more precise structural analysis, in particular, a technique for analyzing block constitution and each segment independently is desired. However, since such aromatic block copolymer is basically low in decomposability, a technique of decomposing almost all polymer structures at high temperature, such as pyrolysis gas chromatography, is ordinarily used, and there is no method for selectively analyzing segments constituting an aromatic block copolymer at all.